Method and apparatus for treatment of wastewater employing membrane bioreactors

ABSTRACT

Methods and apparatus employing membrane filtration in biodegradation processes for treatment of wastewater are described. A bioreactor system is described having an equalization system, a membrane bioreactor system, and a controller. Aeration systems for a membrane bioreactor, such as a mixer, and an ultrafilter subsystem are also described, as is a rotary membrane ultrafilter.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pending patentapplication Ser. No. 09/879,496, filed Jun. 12, 2001, entitled “Methodand Apparatus for Mixing Fluids, Separating Fluids, and SeparatingSolids from Fluids,” by Johnny Arnaud, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to methods and apparatus employingmembrane filtration in biodegradation processes (called “membranebioreactors”) for treatment if wastewater containing organiccontaminates.

[0004] 2. Description of Related Art

[0005] Chemical compounds containing carbon are designated as organiccompounds and may include compounds derived from living organisms.Biodegradable materials are those capable of being decomposed bybiological means as by bacterial action. Biodegradable materials arethose that serve as food for bacteria. The bacteria are naturallyoccurring. Therefore, processes employing biodegradation are seen to be“nature's way” and in many cases preferred over other methods ofremoving organic compounds that contaminate wastewater derived fromindustrial and other processes.

[0006] Bacteria are active only at the limited outer surface of thecontaminants to be consumed as food. The bacteria produce enzymes todisperse the contaminants and increase the amount of surface, and theamount of food, available to them. A different enzyme may be required todisperse each contaminant present.

[0007] When food is available and the right supporting conditions arepresent, bacteria can reproduce in large quantities in very shortperiods of time. Catabolism is the process by which bacteria change, ordecompose, the contaminants into simpler compounds, also known asdestructive metabolism. It is a chemical oxidation-reduction process fororganic carbon removal that is either aerobic (those occurring in thepresents of dissolved oxygen) or anaerobic (those occurring in thecomplete absence of oxygen). The bacteria and the man made systems inwhich the biodegradation processes occur are also designated as eitheraerobic or anaerobic. Both dissolved and solid organic wastes aredecomposed to gases. The gases are carbon dioxide if the process isaerobic or carbon dioxide and methane if anaerobic. The aerobic processis much faster at the destruction of most organic contaminants and isthe primary emphasis of the present invention.

[0008] The organic matter is normally a very small percentage of thecontaminated wastewater and is dispersed throughout the entire contentof the wastewater in which it is contained. The systems in which thebiodegradation processes occur are typically very large to provide theretention time required for the bacteria to reach and consume the smallpercentage of organic waste. It is extremely difficult if not impossibleto supply the dissolved oxygen needed to promote aerobic bacterialactivity in highly diluted system.

[0009] The processes are enhanced when the organic matter can beconcentrated into a smaller quantity of wastewater. A filter capable ofconcentrating the organic matter to an optimum level by removing a largepart of the water would accelerate the biodegradation process andrequire a much smaller system. The suspended organic solids, dissolvedorganic matter, and the bacteria are called “biomass.” The container inwhich the biodegradation occurs is a biological reactor called a“bioreactor.” Suspended solids and dissolved minerals that precipitatefrom the incoming wastewater also adds to the suspended solidsaccumulated in the bioreactor. The filtration system selected forapplication in biodegradation processes is a membrane assembly called an“ultrafilter.” The system in which the membrane is applied to thebiodegradation process is called a “membrane bioreactor” (MBR).Supplying the oxygen required to promote bacterial activity even insmall biological process systems is a major problem experienced by theentire biodegradation process industry on a worldwide basis.

[0010] Generally, membranes are used in reverse osmosis, nanofilters,ultrafilters, and microfilters. Reverse osmosis and nanofiltersmembranes are able to separate dissolved ions from water and arereferred to as semi-permeable membranes. Ultrafilters and microfiltershave porous membranes and accomplish separation mechanically. Theultrafilter can remove suspended solids and dissolved substances with acutoff point by molecular weight depending on the size of the pores.Membranes are synthetically produced from materials selected to havespecific properties. The membranes are manufactured in the form oftubes, hollow fibers, and sheets.

[0011] In all membranes water is kept flowing along the surface of themembrane in a sweeping or washing motion called “cross flow” to preventexcessive concentration of solids on its surface. The cross flow resultsin shearing the solids from the membrane surface and prevents fouling.

[0012] The membranes are assembled in a configuration called a module oran element. The module, or element, is the smallest assembly that can bepurchased, and is, therefore, referred to as the membrane. Applying amembrane coating on the inside of porous tubes produces tubularmembranes. The coating becomes the membrane and the porous tube servesas the backing or reinforcement for the membrane surface. The feedwastewater enters the tube and some of the water is separated from thesolids and passes through the membrane and porous tube. The water thatpasses through the membrane is called “permeate.” The part of thebiomass including wastewater, suspended solids, and dissolved organicsolids that do not pass through the membrane as permeate is called“reject.” The amount of permeate a membrane can produce per unit ofmembrane area is called “flux rate” and is a function of thedifferential pressure across the membrane and the effectiveness of thecross flow at keeping the membrane from fouling.

[0013] In applications where wastewater has high solid concentrations,the tubular membrane has the advantage of allowing high velocity crossflow inside the tubes to sweep the solids and minimize sticking to themembrane surface and reducing the capacity. The result of the deposit onthe membrane surface is called “fouling.” While the tubular membrane isused in the disclosure of the present invention it is understood that itis not intended to be a limitation of the invention.

[0014] Hollow fiber membranes may be very small in diameter. The thinoutside skin is the membrane and the porous layer acting as the supportmedium. Feed water is introduced around the outside of the hollow fiber.The water is separated from the solids as it passes through the thinouter layer, flows through the porous support layer to the inside of thehollow tube, and then out the end. The hollow fiber module contains anenormous amount of fibers that account for the large surface area ofthis type membrane.

[0015] Sheet membranes are made by modifying the surface of a thickersheet to form a dense, microporous film on top and serves as the workingmembrane that actually rejects the solids and large molecular weightsolutions as water flows through. The function of the remaining andthicker part of the sheet is to provide support. The sheet membranes aremade by winding two large sheets in a spiral, called “spiral woundmembranes,” with two membrane surfaces facing each other and placing aspacer between the support sides of the two sheets as they are rolledinto a coil. The spiral wound membrane has not played a significant rollin the wastewater treatment industry. The sheet membranes are also madein the form of discs. The discs are assembled by stacking the discs in amodule. The disc membrane has some application in wastewater treatment.

[0016] Membrane bioreactors have been used commercially for 20 years ormore. The European and other foreign industries appear to be ahead ofthe United States in developing the technology and applying it tobiodegradation processes. The state of technology commercialization iswell documented in “Membrane Bioreactors for Wastewater Treatment,” TomStephenson, Simon Judd, Bruce Jefferson, and Keith Brindle, IWAPublishing, London, UK, ©2000 IWA Publishing and the authors.

[0017] The biological processes that allow the entire biomass to be infree suspension in the wastewater are called “suspended growth”processes. Good mixing is required in suspended growth systems to ensurebacterial contact with the entire organic content of the systems. Inother biological processes fixed structures of material not consumed bybacteria are provided on which the bacteria can grow. Those biologicalprocesses are classified as “fixed film” processes. The wastewatercontaining the organic matter in fixed film processes has to be broughtinto contact with the bacteria on the support structures, therefore,also requiring some form of mixing.

[0018] Membrane bioreactor systems are also identified by the functionof the membranes applied and where they are located in the systems.There are membranes used for separation of biomass, some are submergedin the biomass and used as a fixed film through which bubble-less pureoxygen is supplied to the bacteria attached to the outside of themembranes, and some are used for extracting inorganic materials that mayinhibit the activity of the bacteria in degradation of certain toxiccompounds in wastewater. The methods and apparatus of the presentinvention corrects deficiencies of the biomass separation systems,enhances energy operating efficiency, and may totally replace the needfor most submerged fixed-film membrane bioreactor systems used to supplybubble-less pure oxygen to the bacteria. The extracting membranebioreactors are applied for special purposes and can be used inconjunction with or without the other membrane bioreactor processes.Therefore, extracting membrane bioreactor processes are not addressed inthe present invention.

[0019] In biomass separation bioreactor systems the membranes are usedto separate and concentrate the biomass by removing wastewater. In onetype separation system the membranes are located in a sidestream outsidethe bioreactor. The biomass is drawn from the bioreactor and pumpedthrough the membranes where wastewater is removed as permeate andsuspended organic and mineral solids, dissolved organic matter, andbacteria are retained and returned to the bioreactor more concentrated.In this configuration, the biomass is under pump pressure when flowingthrough the membranes and provides the differential pressure across themembrane.

[0020] In other biomass separation systems the membranes are submergedin the bioreactor. The head pressure of the wastewater on the outside ofthe submerged membranes provides lower but sufficient differentialpressure to drive the wastewater through the membranes and concentratethe biomass in the bioreactor. In some submerged systems the headpressure is supplemented by a suction pump connected to the permeateoutlet side to create a higher differential pressure across themembranes.

[0021] The solids in the biomass (sometimes called “sludge”) build up onand foul the membranes, and the systems must be periodically shutdownand chemically cleaned. The more concentrated the sludge becomes themore often the membranes have to be cleaned. A method of reducing theconcentration of sludge flowing through the membrane would alleviate theclogging and greatly reduce the amount of membrane cleaning required andreduce the cost of chemicals used in the process. Increasing theoperating time between cleaning operations would also reduce the cost ofmanpower and increase the useful life of the costly membranes.

[0022] The bioreactor is typically a tank or vessel in which biologicalreduction of organic matter occurs. The tank is aerated to supply oxygento the bacteria and to help with mixing. Increasing the pressure underwhich the bioreactor operates also increases the amount of oxygen thatcan be dissolved in the water. However, the cost of the bioreactorvessel increases dramatically with increased pressure and size.

[0023] Aeration is a major problem typically experienced by the entirewastewater treatment industry. Hundreds and perhaps thousands of peopleare looking for a better way to provide the oxygen required by bacteriain all types of biodegradation processes including those that employmembrane bioreactors. While separation membrane bioreactors typicallyprovide oxygen by bubbling air through the biomass, the presentinvention brings the bacteria into direct contact with dissolved oxygenby circulating the entire volume of biomass through liquid-gas mixersapplied as dissolved gas generators. Either oxygen in air, pure oxygen,or enriched oxygen can be supplied under pressure to the dissolved gasgenerators by a compressor, bottled oxygen, or membrane separators thatenrich the oxygen by removing nitrogen from atmospheric air.Alternatively, the dissolved gas generators can also draw oxygen bysuction from the atmosphere or from other low-pressure supplies. The useof dissolved oxygen for aeration alleviates the serious problem offoaming typically experienced by bubbling air through the systems.

[0024] A need exists worldwide for an improved apparatus and method ofproviding oxygen to bacteria and reducing sludge fouling of membranes inmembrane bioreactor systems.

[0025] It will become clear to those skilled in the art having thebenefit of this disclosure that the methods and apparatus in accordancewith the present invention overcome, or at least greatly minimize, thedeficiencies of existing membrane bioreactor apparatus and methods.

SUMMARY OF THE INVENTION

[0026] The present invention provides a new method and apparatus forimproving biodegradation of organic wastewater contamination in amembrane bioreactor by minimizing the particle size of solids flowingthrough the membranes to prevent clogging or fouling and by flowing thebiomass through a liquid-gas mixer where the liquid containing thebacteria is saturated with dissolved oxygen and the excess un-dissolvedgases are removed by the mixer to ensure adequate oxygen for thebacteria before returning to the bioreactor.

[0027] An apparatus in accordance with the present invention maygenerally employ an equalization system to consolidate various streamsof wastewater into one with a more consistent flow and level ofcontamination, a membrane bioreactor system where the biodegradationoccurs in a bioreactor vessel with ultrafilters for sidestreamfiltration to remove excess water and concentrate the biomass, and acontroller to monitor and control the process. The apparatus may employliquid-gas mixers as dissolved gas generators in both the equalizationand membrane bioreactor systems to supply dissolved oxygen to thebacteria without bubbling air through the system. A cyclone filter isused to remove suspended solids from the wastewater stream that flowsthrough the ultrafilters to minimize fouling. Where solid particles arelarge, cyclone filters may also be used in both the equalization andmembrane bioreactor systems to remove suspended solids from thewastewater streams that flow through the dissolved gas generators.

[0028] One embodiment of the present invention may employ one or moremixers applied as dissolved gas generators and a cyclone filter upstreamof each mixer to return the bulk of the solids to the equalization tankand allow only the very fine particles and bacteria to flow with theliquid through the mixer and be saturated with dissolved oxygen thenreturned to the equalization tank through a distributor to be remixedwith the solids separated in the cyclone filter. The dissolved oxygen ismonitored, and the number of dissolved gas generators needed to maintainthe range preset in the controller is placed into operation. The numberof dissolved gas generators used depends on the size of the bioreactorsystem. The pH in the equalization tank is also monitored and adjustedto the range preset in the controller.

[0029] Biomass drawn from the bioreactor vessel is also separated intobulk liquid and bulk slurry streams by a cyclone filter. The bulk slurrystream is returned to the bioreactor vessel. The bulk liquid with onlyvery fine particles and bacteria is pumped through the ultrafilterswhere some of the wastewater is removed and all solids and bacteria stayin the remaining bulk liquid stream then flows through a dissolved gasgenerator and is saturated with dissolved oxygen. The bulk liquid streamis then divided downstream of the dissolved gas generator into multiplestreams and returned to the bioreactor and mixed with biomassre-circulating from the vessel in a number of mixers dispersed atvarious levels in the bioreactor vessel.

[0030] Dissolved oxygen is monitored and adjusted by the controller asrequired. Biomass that cannot be consumed by bacteria, such as minerals,is periodically purged from the bioreactor when present.

[0031] Another embodiment of the present invention employs one or moredissolved gas generators with all biomass flowing through the dissolvedgas generators to be saturated with dissolved oxygen then returned tothe equalization tank and dispersed through distributors at variouslevels in the tank. When the concentration of solids in the incomingstreams of wastewater is low, no cyclone filter is needed for water inthe equalization tank. The dissolved oxygen is monitored, and the numberof dissolved gas generators needed to maintain the range preset in thecontroller is placed into operation. The number of dissolved gasgenerators needed in the system depends on the size of the bioreactorsystem. The pH in the equalization tank is also monitored and adjustedto the range preset in the controller. Biomass drawn from the bioreactorvessel is separated into bulk liquid and bulk slurry streams by acyclone filter. The bulk slurry stream is returned to the bioreactorvessel. The bulk liquid with only very fine particles and bacteria ispumped through the ultrafilter where some of the water is removed andall solids and bacteria are returned to the bioreactor vessel with theremaining bulk liquid.

[0032] Multiple dissolved gas generators may be used for redundancy inorder to continue operating the system if one of the mixers fails. Withmultiple dissolved gas generators the number in operation can be variedto provide the dissolved oxygen needed. Dissolved oxygen is monitoredand adjusted by the controller as required. Biomass that cannot beconsumed by bacteria, such as minerals, is periodically purged from thebioreactor when present.

[0033] Another embodiment of the present invention also employs one ormore mixers applied as dissolved gas generators with all biomass flowingthrough the mixer to be saturated with dissolved oxygen then returned tothe equalization tank and dispersed through distributors at variouslevels in the tank. The dissolved oxygen is monitored, and the number ofdissolved gas generators needed to maintain the range preset in thecontroller is placed into operation. The number of dissolved gasgenerators needed in the system depends on the size of the bioreactorsystem. The pH in the equalization tank is also monitored and adjustedto the range preset in the controller. Biomass drawn from the bioreactorvessel is separated into bulk liquid and bulk slurry streams by acyclone filter. The bulk slurry stream is returned to the bioreactorvessel. The bulk liquid with only fine particles and bacteria flows intoa sub tank. Bulk liquid is drawn from the sub tank and pumped throughthe membrane ultrafilter where some of the water is removed and allsolids and bacteria are returned to the bioreactor vessel with theremaining bulk liquid. There are two aeration loops with two mixersemployed as dissolved gas generators in each loop. A stream of bulkliquid is drawn from the sub tank and pumped through two mixers in eachloop and dispersed through distributors at various levels in thebioreactor vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 depicts a schematic representation of a membrane bioreactorsystem identifying major system component and illustrating the flowpattern through cyclone filters to separate solids from the liquidbefore flowing through membrane ultrafilters and aerators in accordancewith the present invention.

[0035]FIGS. 2A and 2B depict a combination mixer and distributor inaccordance with the present invention. FIG. 2A illustrates thehorizontal flow of the fluid as it enters the mixer-distributor. FIG. 2Billustrates a vertical cutaway view of the mixer identifying majorcomponents and showing the flow of the fluids as they are being mixed.

[0036]FIGS. 3A and 3B are schematics illustrating a typical cyclonefilter. FIG. 3A illustrates the horizontal flow of the fluid as itenters the cyclone filter. FIG. 3B is a fluid flow diagram illustratingthe vertical flow of the fluid through the components of the cyclonefilter.

[0037]FIGS. 4A and 4B are fluid diagrams of a cyclone filter employing aspiral-grooved ring mounted on the outside of the housing to divide theentering fluid and inject the fluid in high velocity multiple streamsinto and at a tangent to a cylinder above the cone shaped housing. FIG.4A illustrates the horizontal flow of the fluid as it enters the cyclonefilter. FIG. 4B is a fluid flow diagram illustrating the vertical flowof fluid through the components of the cyclone filter.

[0038]FIGS. 5A, 5B, and 6 are fluid diagrams of a fluid mixer used as adissolved gas generator employing a radial-grooved ring, an orifice ringpositioned with the orifice ports over each groove in order to inject agas into each stream, and an impact zone for saturating liquids withdissolved gases. FIG. 5A illustrates the horizontal flow of the liquidas it enters the fluid mixer and flows through the radial-grooved ring.FIG. 5B illustrates the horizontal flow of the fluid as it enters thefluid mixer and flows through the radial-grooved ring with an orificering positioned with the orifice ports over each groove in order toinject a gas into each stream. FIG. 6 is a fluid flow diagramillustrating the vertical flow of fluid through the components of thefluid mixer.

[0039]FIGS. 7A and 7B provide three-dimensional illustrations of atypical radial-grooved ring and a combination venturi-orifice ring usedin the fluid mixer.

[0040]FIG. 8 is a fluid diagram of fluid mixer employing aradial-grooved ring; a combination venturi-orifice ring positioned withthe venturi and orifice ports in each groove in order to draw a secondfluid into each stream, and an impact zone for mixing the variousfluids.

[0041]FIG. 9 is a schematic illustration of an aeration system forsupplying pure oxygen and recycling any excess pure oxygen supplied to amembrane bioreactor system.

[0042]FIG. 10 is a fluid diagram of another embodiment of a membranebioreactor system employing a cyclone filter to separate large solidparticles from the stream flowing through the membrane ultrafilter andmultiple fluid mixers applied as dissolved gas generators for deliveringoxygen to the microorganisms in both the equalization and bioreactortanks, also with cyclone filter pretreatment.

[0043]FIG. 11 is a fluid diagram of another embodiment of a membranebioreactor system employing a cyclone filter to separate large solidparticles from the stream before flowing through the membraneultrafilter and multiple fluid mixers applied as dissolved gasgenerators for delivering oxygen to the microorganisms in the bioreactorvessel.

[0044]FIG. 12 depicts a schematic illustration of a third embodiment ofa membrane bioreactor fluid treatment system.

[0045]FIG. 13A illustrates a top view of the rotating membraneultrafilter 303 and shows where a vertical cross sectional view A-A istaken and shown in a subsequent illustration.

[0046]FIG. 13B illustrates a side elevation view of the rotatingmembrane ultrafilter 303 to identify general components. The rotatingmembrane ultrafilter 303 consists of lower housing 305, a membrane driveassembly 307, a motor 309, a wastewater inlet 306, a reject water outlet304, and a permeate outlet 308.

[0047]FIG. 14 depicts a sectional view A-A taken from FIG. 13A.

[0048]FIG. 15 depicts a schematic illustration of the membrane driveassembly.

[0049]FIG. 16 is an elevation view of a membrane.

[0050]FIG. 17 illustrates the cross section A-A of the membrane of FIG.16.

[0051]FIG. 18A illustrates a top view of a rotating membraneultrafilter.

[0052]FIG. 18B illustrates a side elevation view of the rotatingmembrane ultrafilter.

[0053]FIG. 19 depicts a sectional view A-A taken from FIG. 18A.

[0054]FIG. 20 provides a view downward inside a lower housing of oneembodiment of the present invention.

[0055]FIG. 21 provides an enlarged schematic illustration of a membranedrive assembly.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0056] Illustrative embodiments of the invention are described below asthey might be employed in the treatment of wastewater using membranebioreactors. In the interest of clarity, not all features of animplementation are described in this specification. It will of course byappreciated that in the development of any such actual embodiment,numerous implementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

[0057] Further aspects and advantages of the various embodiments of theinvention will become apparent from consideration of the followingdescription and drawings.

[0058]FIG. 1 depicts in schematic illustration a flow diagram of anexemplary membrane bioreactor fluid treatment system 1 forbiodegradation of organic contaminants in wastewater in accordance withone embodiment of the present invention. The arrows in the pipingindicate the direction of fluid flow. The membrane bioreactor fluidtreatment system consists of an equalization system 2 to merge variousstreams of wastewater and equalize the flow and contaminant level intoone stream, a membrane bioreactor system 3 where the biomass isconcentrated and most of the biodegradation occurs, and a controller 4to monitor and control the operation.

[0059] The equalization system 2 consists of a wastewater collectiontank 5 where various streams of water are consolidated into one biomass.The collection tank 5 is provided with a wastewater inlet 19, a vent 21,and level sensor 20.

[0060] There are two systems for supplying dissolved oxygen to promotethe activity of the aerobic bacteria in the collection tank 5 and killanaerobic bacteria to control odor. One of the dissolved oxygen supplysystems generally consists of a circulating pump 8, a cyclone filter 9where the biomass is separated into bulk liquid and bulk slurry streams,a mixer applied as a dissolved gas generator 14, and a distributor 11 todisperse the fluid saturated with dissolved oxygen in the collectiontank 5. Operation of the cyclone filter 9 and the dissolved gasgenerator 14 are described in detail in following discussions.

[0061] Circulating pump 8 draws biomass from collection tank 5 throughoutlet port 6 and injects it at high pressure into cyclone filter 9. Thebiomass is separated in the cyclone filter 9 into a bulk slurry streamthat exits the filter as an underflow and a bulk liquid stream as anoverflow. The bulk slurry flows out the bottom of the cyclone filter 9through piping 16 and returns to the collection tank 5 through inletport 17. The bulk liquid flows out of the top of the cyclone filter 9through piping 10 and flows into dissolving gas generator 14 where theliquid is saturated with dissolved oxygen and dispersed inside thecollection tank 5 through distributor 11.

[0062] The second dissolved gas supply system generally consists of acirculating pump 28, a cyclone filter 27 where the biomass is separatedinto bulk liquid and bulk slurry streams, a mixer applied as a dissolvedgas generator 22, and a distributor 23 to disperse the fluid saturatedwith dissolved oxygen in the collection tank 5. Operation of the cyclonefilter 27 and the dissolved gas generator 22 are also described indetail in following discussions.

[0063] Circulating pump 28 draws biomass from collection tank 5 throughoutlet port 29 and injects it at high pressure into cyclone filter 27.The biomass is separated in the cyclone filter 27 into a bulk slurrystream that exits the filter as an underflow and a bulk liquid stream asan overflow. The bulk slurry flows out the bottom of the cyclone filter27 through piping 7 and returns to the collection tank 5 through inletport 18. The bulk liquid flows out of the top of the cyclone filter 27through piping 25 and flows into dissolved gas generator 22 where theliquid is saturated with dissolved oxygen and dispersed inside thecollection tank 5 through distributor 23.

[0064] The first dissolved gas supply system is installed in the lowerpart of the collection tank 5 and is the primary supply when thecollection tank is not full. A pH sensor 15 installed in piping 10provides a signal to the controller. The amount of dissolved oxygen inthe equalization system 2 is monitored before and after dissolved gasgenerator 14 by sensors 12 and 13 respectively. The consolidated biomassis pumped out of the collection tank by a pump 26 and transferred to thebioreactor system 3 through piping 30 where it enters the bioreactorthrough inlet port 39.

[0065] The bioreactor system 3 consists generally of bioreactor vessel33 in which the degradation occurs; a cyclone filter 59 for separationof the biomass into bulk liquid and bulk slurry streams; ultrafiltermembranes 48, 49, and 50 for removing liquid and concentrating thebiomass, a mixer applied as a dissolved gas generator 42 to saturate theliquid with oxygen, mixers 37 to mix the bulk liquid saturated withdissolved oxygen and the biomass from the bioreactor vessel 33 anddisperse the mixture into the bioreactor vessel 33, and an oxygen supply58.

[0066] In operation biomass is drawn by pump 61 from the bioreactorvessel 33 through outlet port 63 and injected at high pressure intocyclone filter 59. The biomass is separated in the cyclone filter 59into a bulk slurry stream that exits the filter as an underflow and abulk liquid stream that exits the filter as an overflow. The bulk slurrystream flows out the bottom of the cyclone filter 59 through piping 60and returns to the bioreactor vessel 33 through inlet port 38. The bulkliquid with very fine particles and bacteria flows out the top of thecyclone filter 59 through piping 54 and flows through ultrafilters 48,49, 50, and membrane interconnecting piping 46 and 56 and out theultrafilters through piping 43.

[0067] Water removed from the biomass by the ultrafilter is dischargedthrough piping 57. The bulk liquid from piping 43 flows into thedissolved gas generator 42 where it is saturated with oxygen. From thedissolved gas generator 42 the saturated liquid flows through pipingmanifold 51 where the liquid is divided into four streams and fed intomixers 37 through piping laterals 53. Biomass is drawn by pump 32 fromthe bioreactor vessel 33 through outlet port 31 and pumped throughpiping manifold 35 where the biomass is divided and flows into mixers 37and mixed with the bulk liquid from the dissolved gas generator 42 anddispersed at various levels in the bioreactor vessel 33.

[0068] The bioreactor vessel is vented 41 to operate at atmosphericpressure. The level of the biomass is monitor by a level sensor 40.Either oxygen in air, pure oxygen, or enriched oxygen is supplied underpressure to the dissolved gas generator 42 by a compressor (not shown),bottled oxygen 58, or membrane separator to remove nitrogen fromatmospheric air (not shown). While membrane bioreactors typicallyprovide oxygen by bubbling air through the biomass, the presentinvention brings the bacteria into direct contact with dissolved oxygenby circulating the entire volume of biomass through liquid-gas mixersapplied as dissolved gas generators. Dissolved oxygen is monitored by asensor 62 to determine the amount of oxygen in the biomass upstream ofpump 61 and a sensor 47 downstream of dissolved gas generator 42. Theuse of dissolved oxygen for aeration alleviates the serious foamingtypically experienced by bubbling air through the systems. A sensor 55downstream of pump 61, sensor 52 upstream of the ultrafilters, andsensor 44 downstream of the ultrafilters monitor system pressure.

[0069] Biomass that cannot be consumed by bacteria, such as minerals, isurged from the system through valve 34.

[0070] The mixers 37 mix the returning saturated bulk liquid withbiomass in the bioreactor vessel. The mixers applied as dissolved gasgenerators 14, 22, and 42 saturate the fluid with dissolved oxygen tosupply the bacteria. The cyclone filters 9, 27, and 59 separate thebiomass stream into bulk liquid and bulk slurry streams. The mixers andthe cyclone filters may correspond structurally and functionally to theradial-grooved ring mixer and the spiral-grooved ring cyclone filterdisclosed in co-pending patent application Ser. No. 09/879,496, filedJun. 12, 2001, in the name of Johnny Arnaud and assigned to the sameassignee as the present application. Mixers 37 are shown in FIGS. 2A and2B. Cyclone filters 9, 27, and 59 are shown in FIGS. 3A-4B. Mixers 14,22, and 42 applied as dissolved gas generators are shown in FIGS. 5A-8.While the radial-grooved ring mixers and the cyclone filters aredescribed herein, the foregoing co-depending application is herebyincorporated herein by reference and can be referred to for furtherstructural detail.

[0071]FIGS. 2A and 2B illustrate the mixers 37 in the membranebioreactor vessel 33 of FIG 1. FIG. 2A depicts a horizontal crosssectional view of the fluid inlet to the fluid mixer 37 illustrating theradial-groove ring 65, the distribution channel 66, the eight radialgrooves 67, the position of orifices 68 over the radial grooves 67, andan impact zone 69 to which radial grooves 67 are directed.

[0072]FIG. 2B provides a vertical cross sectional view of the fluidmixers 37 assembly consisting of top inlet housing 70, a plate withorifices 71, and radial-grooved ring 65 with and impact zone 69 combinedwith a lower distributor with multiple outlets 72. The arrows indicatethe direction of fluid flow. The saturated bulk fluid from the dissolvedgas generator 42 enters the mixer 37 from the top inlet housing 70 andflows through orifices 71 into the radial grooves 67 to be mixed withthe biomass. The biomass from the bottom of the bioreactor vessel 33enters the mixer through inlet 64, flows around the distribution channel66, and is injected at high velocity through the radial grooves 67 andmixed with the saturated bulk fluid entering from the orifices 71 andinto the impact zone 69. The biomass mixed with saturated bulk fluid isdispersed into the bioreactor vessel 33 by the multiple outlets 72.

[0073]FIGS. 3A and 3B are schematics illustrating a typical cyclonefilter. FIG. 3A illustrates the horizontal flow at the inlet 73 of anexisting cyclone filter that may be used to separate suspended solidsfrom wastewater by using centrifugal force. FIG. 3B illustrates thevertical flow through the components of the filter. The arrows indicatethe direction of flow.

[0074] The general features of this type of conventional cyclone filterinclude an inlet 73, a vertical cylinder 75 in which water cancirculate, a lower cone 78, a sludge outlet 79 sometimes referred to asan orifice, and a short outlet cylinder 77 sometimes referred to as avortex finder with the inside of the vortex finder 77 serving as thefluid outlet 76. Water containing the solid particles to be removedenters the filter through inlet 73 at the velocity selected for thespecific size of the filter and injected as a single jet into the filtertangent into the diameter of the cylinder 75. The injected water causesthe water 74 inside the filter to circulate creating a centrifugal forcethat moves the suspended solid particles to the outside diameter of thefilter housing as it spirals downward and causes a low pressure in thecenter of the circulating stream. The water flow reverses and flows upthe center of the circulating stream and out the filter though outlet 76in the vortex finder 77. The solid particles collect in the lowersection of the cone 78 and flow out of the filter through the sludgeoutlet 79.

[0075]FIGS. 4A and 4B illustrate a type of spiral-grooved ring cyclonefilter 9, 27, or 59 that may be used to separate the biomass stream intobulk liquid and bulk slurry streams. The cyclone filter consists of aninlet 80, a distribution channel 85, a spiral-grooved ring 81 withmultiple grooves 83, a cylinder 87 serving as an outer diameter of adown-flow annulus 82, an inner short cylinder or short skirt 86 servingas the inside diameter of the down-flow annulus 82, a lower cone 90, acone outlet 91 for discharging solid particles separated from the fluid,and a fluid outlet 84.

[0076]FIG. 4A illustrates the horizontal flow of the fluid as it entersthe cyclone filter 9, 27, or 59. FIG. 4B illustrates the vertical flowpattern of the fluid through the components of the filter. The arrowsindicate the direction of fluid flow. Fluid enters the cyclone filter 9,27, or 59 through inlet 80 and flows into the distribution channel 85 inboth directions around the outside of the spiral-grooved ring 81. Thefluid from the distribution channel 85 is divided and flows into sixspiral grooves 83 where its velocity is increased then injected into anarrow down-flow annulus 82. The down-flow annulus 82 allows the fluidto be injected at a velocity much higher than filters with no annulus 82without interfering with the outgoing fluid. The fluid flows downward ina spiral motion 88. The circulating fluid causes a vortex 89 to form atthe low-pressure center. As the fluid flows down the lower cone 90 it isforced to the center and upward through the outlet 84. With the innerskirt 86 dividing the incoming and outgoing fluids, the outlet 84 can bemuch larger without the need for a vortex finder. Solid particlesseparated from the fluid are discharged through the outlet 91 into acollection chamber (not shown) or other receptacle.

[0077] FIGS. 5A-6 depict a fluid mixer applied as a dissolved gasgenerator 42 employing the dynamic forces of fluid flow obtained with aradial-grooved ring where pressurized gas is used as an oxygen supply58. FIG. 5A depicts a horizontal cross sectional view of the liquidinlet to the dissolved gas generator 42 illustrating the donut housing92 with the inlet 93, the distribution channel 94, the radial-groovedring 95 with 8 radial grooves 96, and an impact chamber 97 or zone towhich the radial grooves 96 are directed.

[0078]FIG. 5B also provides a horizontal cross sectional view of thedissolved gas generator 42 with an orifice ring 98 positioned with theorifice ports 99 over the radial-grooves 96. The arrows indicate thedirection of fluid flow. FIG. 6 provides a vertical cross sectional viewof the fluid mixer 96 assembly consisting of a cylindrical donut housing92, an orifice ring 98, a radial-grooved ring 95, a lower cylinder 91,and a lower cap 90. The cylindrical donut housing 92 has a gasseparation chamber 105 to separate excess gases from the liquids so thegases can be discharged while retaining the liquid.

[0079] The center of the radial-grooved ring 95 serves as an impact zone97 into which the multiple streams of the liquid-gas mixture flowing athigh velocity are directed to collide with each other. An inletgas-metering valve 107 connected to the gas inlet 106 of the cylindricaldonut housing 92 regulates the amount of gas supplied during operation.An outlet gas-metering valve 104 connected to the gas outlet 103 of thecylindrical donut housing 92 regulates the amount of gas discharged fromthe device during operation.

[0080] Referring to FIG. 5B, the arrows indicate the direction of liquidflow. The liquid enters the fluid mixer 42 through the inlet 93 andflows into the distribution channel 94 in both directions around theradial-grooved ring 95. The liquid is divided and flows into the radialgrooves 96 under the orifice ring 98 where gas is injected into each ofthe high velocity streams. The liquid-gas mixture in each groove is theninjected into the impact zone 97.

[0081] Referring to FIG. 6, again the liquid enters through inlet 93 andflows into the distribution channel 94 around the radial-grooved ring95. The liquid then flows through the radial grooves 96 where gas isinjected through the orifice ports 99 into each liquid stream. Theliquid-gas mixture in each of the grooves 96 is then injected at highvelocity into the impact zone 97 to collide with each other. The liquidbecomes saturated with gas at this point. The inlet gas-metering valve107 regulates the amount of gas supplied.

[0082] The saturated liquid 102 flows downward out of the impact zone 97and into the larger area of the lower cylinder 91 where the velocity isdecreased. The excess gas bubbles 108 flow upward and return to theimpact zone 97. The saturated liquid 102 continues to flow downward andexits through the outlet 109. The excess bubbles flow up through theimpact zone 97, and the gas is separated from the liquid in theseparation chamber 105 and released from the unit through the outletgas-metering valve 104.

[0083] The amount of gas retained in the separation chamber 105regulates the liquid level in the apparatus. The amount of gas releasedis adjusted to maintain the liquid level just above the impact zone 97,and only a small amount of gas has to be released from the chamber 105.The fluid mixer 42 is extremely effective at saturating liquid with gaswith only five parts that can be manufactured in many sizes at low cost.It can be manufactured in metal or in plastic either machined orinjected molded.

[0084] FIGS. 7A-8 depict a fluid mixer applied as a dissolved gasgenerator 14 and 22 employing dynamic forces of fluid flow obtained witha radial-grooved ring where atmospheric air or other low pressure gas isused as an oxygen supply and drawn into the mixer by venturi suction.FIGS. 7A and 7B provide three-dimensional illustrations of a typicalradial-grooved ring 114 and a combination venturi-orifice ring 111having 12 orifices 110 and 12 venturi 112 to fit into the radial grooves113 of the radial-grooved ring 114.

[0085]FIG. 8 provides a vertical cross-sectional view of the fluid mixer14 and 22 assembly consisting of a cylindrical donut housing 119, acombination venturi-orifice ring 111, a radial-grooved ring 114, a lowercylinder 116, and a lower cap 115. The cylindrical donut housing 119 hasa gas separation chamber 122 to separate excess gases from the liquidsso the gases can by discharged while retaining the liquid. The center ofthe radial-grooved ring 114 serves as an impact zone 126 into which themultiple streams of the liquid-gas mixture flowing at high velocity aredirected to collide with each other. An inlet gas-metering valve 124connected to the gas inlet 123 of the cylindrical donut housing 119regulates the amount of gas supplied during operation. An outletgas-metering valve 121 connected to the gas outlet 120 of thecylindrical donut housing 119 regulates the amount of gas dischargedfrom he device during operation.

[0086] Referring to FIG. 8, the liquid enters through inlet 118 andflows into the distribution channel 125 around the radial-grooved ring114. The liquid then flows through the radial grooves 113 where gas isdrawn through the orifice ports 110 into each liquid stream as theliquid flows by the venturi. The liquid-gas mixture in each of thegrooves 113 is then injected at high velocity into the impact zone 126to collide with each other. The liquid becomes saturated with gas atthis point. The inlet gas-metering valve 124 regulates the amount of gassupplied.

[0087] The saturated liquid 117 flows downward out of the impact zone126 and into the larger area of the lower cylinder 116 where thevelocity is decreased. The excess gas bubbles 127 flow upward and returnto the impact zone 126. The saturated liquid continues to flow downwardand exits through the outlet 128. The excess bubbles flow up through theimpact zone 126, and the gas is separated from the liquid in theseparation chamber 122 and released from the unit through the outletgas-metering valve 121.

[0088] The amount of gas retained in the separation chamber 122regulates the liquid level in the apparatus. The amount of gas releasedis adjusted to maintain the liquid level just above the impact zone 126,and only a small amount of gas has to be released from the chamber 122.The fluid mixer 14 and 22 is extremely effective at saturating liquidswith gases with only five parts that can be manufactured in many sizesat low cost. It can be manufactured in metal or in plastic eithermachined or injected molded.

[0089]FIG. 9 provides a schematic illustration of an aeration system, orsub system, 130 for a membrane bioreactor that supplies pure oxygen forsaturation of the biomass and recycles the excess oxygen discharged fromthe mixer without releasing any of the oxygen to the atmosphere.

[0090] The aeration system 130 consists generally of a mixer with acombination venturi-orifice ring applied as a dissolved gas generator135, a pure oxygen supply 142 with a shutoff valve 141 and a pressureregulator 140, a low-pressure storage tank 132, and associated piping.In operation, biomass from the membrane bioreactor system (not shown)enters the dissolved gas generator 135 under pressure through inlet line134 and flows through the dissolved gas generator 135 where the biomassis saturated with pure oxygen and exits through the outlet line 133. Asthe biomass flows passed the venturi in the dissolved gas generator 135,pure oxygen is drawn from the low-pressure storage tank 132 through thegas supply line 137 and saturates the biomass as described in thediscussion of FIG. 8. The excess pure oxygen released from the dissolvedgas generator 135 is returned to the low-pressure tank 132 throughoutlet line 136. Only a small percentage of the pure oxygen used tosaturate the biomass is discharged from the dissolved gas generator 135and returned to the low-pressure tank 132. The pure oxygen supply 142maintains the pressure preset by the pressure regulator 140 as indicatedby pressure gage 138 in the low-pressure tank 132. Moisture thataccumulates in the low-pressure tank is discharged through drain valve131. Only the oxygen needed to supply the bacteria is consumed by thisaeration system 130 making it feasible to use pure oxygen in manymembrane bioreactor systems.

[0091]FIG. 10 depicts a schematic illustration of another embodiment ofa membrane bioreactor fluid treatment system 143 for biodegradation oforganic contaminants in wastewater in accordance with one embodiment ofthe present invention. The arrows in the piping indicate the directionof fluid flow. The membrane bioreactor fluid treatment system 143consists of an equalization system 144 to merge various streams ofwastewater and equalize the flowrate and contaminant level into onestream, a membrane bioreactor system 145 where the biomass isconcentrated and biodegradation occurs, and a controller 146 to monitorand control the operation.

[0092] The equalization system 144 consists of a wastewater collectiontank 147 where various streams of water are consolidated into onebiomass. The collection tank 147 is provided with a wastewater inlet156, a vent 158, and level sensor 157.

[0093] There are two systems for supplying dissolved oxygen to promotethe activity of the aerobic bacteria in the collection tank 147 and killanaerobic bacteria to control odor. The first dissolved gas supplysystem in installed in the lower part of the collection tank 147 and isthe primary supply when the collection tank is not full. The firstdissolved oxygen supply system generally consists of a circulating pump149, a mixer applied as a dissolved gas generator 155, and a distributor151 to disperse the fluid saturated with dissolved oxygen in thecollection tank 147.

[0094] Operation of the dissolved gas generator 155 is described indetail in the discussion of FIG. 8. Circulating pump 149 draws biomassfrom collection tank 147 through outlet port 148 and pumps it throughpiping 150 into dissolved gas generator 155 where the liquid issaturated with dissolved oxygen and disperse inside the collection tank147 through distributor 151. A pH sensor 154 installed in piping 150provides a signal to the controller 146. The amount of dissolved oxygenin the equalization system 144 is monitored before and after dissolvedgas generator 155 by sensors 152 and 153 respectively.

[0095] The second dissolved gas supply system generally consists of acirculating pump 164, a mixer applied as a dissolved gas generator 159,and a distributor 160 to disperse the fluid saturated with dissolvedoxygen in the collection tank 147. Operation of the gas generator 159 isdescribed in detail in the discussion of FIG. 8. Circulating pump 164draws biomass from collection tank 147 through outlet port 165 and pumpsit through piping 162 and into dissolved gas generator 159 where theliquid is saturated with dissolved oxygen and disperse inside thecollection tank 147 through distributor 160. The consolidated biomass ispumped out of the collection tank 147 by a pump 163 and transferred tothe membrane bioreactor system 145 through piping 166 where it entersthe bioreactor vessel 167 through inlet port 183.

[0096] The membrane bioreactor system 145 consists generally ofbioreactor vessel 167 in which the biodegradation occurs, four aerationsub systems to supply dissolved oxygen to the bacteria, and anultrafilter sub system to concentrate the biomass in the bioreactorvessel 167 by removing some of the liquid and retaining all suspendedsolids including bacteria.

[0097] The bioreactor vessel 167 is sized to provide the retention timeneeded for biodegradation of the specific organic contaminants in thewastewater to be treated. The retention time required may typically varyfrom 6 to 24 hours, again, depending on the organic contaminants in thewastewater. The bioreactor vessel 167 is vented 182 to operate atatmospheric pressure. A level sensor 184 monitors the level of thebiomass in the reactor vessel 167.

[0098] The four aeration systems are positioned to distribute thesaturated biomass at various levels when saturated with oxygen andreturned to the bioreactor vessel 167. The first aeration sub systeminstalled at the lowest level in the bioreactor vessel 167 generallyconsists of a pump 206, a mixer applied as a dissolved gas generator197, a gas shutoff valve 198, a distributor 203, and associated piping.

[0099] Operation of the dissolved gas generator 197 is described indetail in the discussion of FIGS. 5A-6. Circulating pump 206 drawsbiomass from the bioreactor vessel 167 through outlet port 205 and pumpsit through piping 207 into dissolved gas generator 197 where the liquidis saturated with dissolved oxygen and dispersed inside the bioreactorvessel 167 through distributor 203.

[0100] The second aeration sub system installed at the second level inthe bioreactor vessel 167 generally consists of a pump 169, a mixerapplied as a dissolved gas generator 176, a gas shutoff valve 175, adistributor 173, and associated piping. Operation of the dissolved gasgenerator 176 is described in detail in the discussions of FIGS. 5A-6.Circulating pump 169 draws biomass from the bioreactor vessel 167through outlet port 170 and pumps it through piping 172 into dissolvedgas generator 176 where the liquid is saturated with dissolved oxygenand dispersed inside the bioreactor vessel 167 through distributor 173.

[0101] The third aeration sub system installed at the third level in thebioreactor vessel 167 generally consists of a pump 217, a mixer appliedas a dissolved gas generator 187, a gas shutoff valve 188, a distributor196, and associated piping. Operation of the dissolved gas generator 187is described in detail in the discussions of FIGS. 5A-6. Circulatingpump 217 draws biomass from the bioreactor vessel 167 through outletport 204 and pumps it through piping 192 into dissolved gas generator187 where the liquid is saturated with dissolved oxygen and dispersedinside the bioreactor vessel 167 through distributor 196.

[0102] The fourth aeration sub system installed at the fourth level inthe bioreactor vessel 167 generally consists of a pump 168, a mixerapplied as a dissolved gas generator 180, a gas shutoff valve 181, adistributor 177, and associated piping. Operation of the dissolved gasgenerator 180 is described in detail in the discussions of FIGS. 5A-6.Circulating pump 168 draws biomass from the bioreactor vessel 167through outlet port 171 and pumps it through piping 179 into dissolvedgas generator 180 where the liquid is saturated with dissolved oxygenand dispersed inside the bioreactor vessel 167 through distributor 177.

[0103] The operation of the four aeration systems is monitor andcontrolled by the controller 146. Oxygen is supplied by the gas supply212 as air by a compressor (not shown), as pure oxygen, or as enhancedoxygen by a nitrogen removal membrane (not shown). The sensor 216located in the line upstream of pump 215 monitors the amount ofdissolved oxygen in the biomass as it flows out of the bioreactor vessel167 and is used by the controller 146 to determine the amount ofdissolved oxygen remaining in the volume of biomass in the reactorvessel 167. Sensors 174, 178, 193, and 202 monitor the amount ofdissolved oxygen in the biomass as it flows out of each dissolved gasgenerator 176, 180, 187, and 197 and is used by the controller todetermine the amount of dissolved oxygen being added to the biomass inthe reactor vessel 167. By comparing the amount of dissolved oxygenremaining in the biomass in the bioreactor vessel 167 and the amountbeing added by the dissolved gas generators the controller can regulatorthe total amount of dissolved oxygen in the biomass to within a rangepreset in the controller 146 and startup or shutdown individualdissolved gas generators by turning the associated circulating pumps168, 169, 206, or 217 on or off and opening or closing the correspondinggas supply valves 175, 181, 188, or 198. The use of dissolved oxygen foraeration alleviates the serious problem of foaming typically experiencedby bubbling air through the systems.

[0104] The ultrafilter sub system consists generally of a circulatingpump 215; a cyclone filter 209 for separation of the biomass into bulkliquid and bulk slurry streams; ultrafilters 199, 200, and 201 forremoving liquid and concentrating the biomass; and associated piping. Inoperation biomass is drawn by pump 215 from the bioreactor vessel 167through outlet port 218 and injected at high pressure into cyclonefilter 209. The biomass is separated in the cyclone filter 209 into abulk slurry stream that exits the filter as an underflow and a bulkliquid stream that exits the filter as an overflow. The bulk slurrystream flows out the bottom of the cyclone filter 209 through piping 189and returns to the bioreactor vessel 167 through inlet port 186.

[0105] The bulk liquid with very fine particles and bacteria flows outthe top of the cyclone filter 209 and flows through ultrafilters 199,200, 201, and membrane interconnecting piping 194 and 210 and out theultrafilters through piping 190. Water removed from the biomass by theultrafilters is discharged through piping 211. The bulk liquid frompiping 190 is returned to the bioreactor vessel 167 through inlet port185. Sensor 214 downstream of pump 215, sensor 208 upstream of theultrafilter 199, and sensor 195 downstream of the membrane ultrafilter201 monitor the system pressure. From the pressures the performance ofthe ultrafilters 199, 200, and 201 can be determined and used as anindication of when they need to be cleaned.

[0106] Biomass that cannot be consumed by bacteria, such as minerals, isperiodically purged from the system through valve 213.

[0107]FIG. 11 depicts a schematic illustration of another embodiment ofa membrane bioreactor fluid treatment system 219 for biodegradation oforganic contaminants in wastewater in accordance with one embodiment ofthe present invention. The arrows in the piping indicate the directionof fluid flow. The membrane bioreactor fluid treatment system consistsof an equalization system 144 to merge various streams of wastewater andequalize the flowrate and contaminant level into one stream, a membranebioreactor system 221 where the biomass is concentrated andbiodegradation occurs, and a controller 222 to monitor and control theoperation. The equalization system 144 is the same equalization system144 as the one in the membrane bioreactor fluid treatment system 143illustrated in FIG. 10 and incorporated here by reference to the FIG. 10discussions.

[0108] The membrane bioreactor system 221 consists generally ofbioreactor vessel 223 in which the biodegradation occurs, an aerationsystem to supply dissolved oxygen and saturate the bulk liquid with pureoxygen to promote activity of the bacteria, a biomass separation subsystem to divide the biomass into bulk slurry and bulk liquid streams,and an ultrafilter sub system to concentrate the biomass in thebioreactor vessel 223 by removing some of the liquid and retaining allsuspended solids including bacteria. Using pure oxygen increases thesaturation concentration by approximately 4.7 times that available byusing air.

[0109] The bioreactor vessel 223 is sized to provide the retention timeneeded for biodegradation of the specific organic contaminants in thewastewater to be treated. The retention time required may typically varyfrom 6 to 24 hours, again, depending or the organic contaminants in thewastewater. The bioreactor vessel 223 is vented 233 to operate atatmospheric pressure. A level sensor 235 monitors the level of thebiomass in the reactor vessel 223.

[0110] The biomass separation sub system consists generally of a pump250, a cyclone filter 256, a bulk liquid storage tank 258, andassociated piping. In operation biomass is drawn by pump 250 from thebioreactor vessel 223 through outlet port 248 and injected at highpressure into the cyclone filter 256. The biomass is separated in thecyclone filter 256 into a bulk slurry stream that exits the filter as anunderflow and a bulk liquid stream that exits the filter as an overflow.The bulk slurry stream flows out the bottom of the cyclone filter 256through piping 257 and returns to the bioreactor vessel 223 throughinlet port 237. The bulk liquid with very fine particles and bacteriaflows out the top of the cyclone filter 256 and flows into a bulk liquidstorage tank 258 to be used in the aeration and ultrafilter sub systems.

[0111] The aeration system consists of two aeration sub systems with twopumps and four mixers each and a pure oxygen supply and recycling subsystem. The first aeration sub system consists generally of a pump 252,two mixers applied as dissolved gas generators 229 and 231, andassociated piping. In operation bulk liquid is drawn by pump 252 fromthe bulk liquid storage tank 258 through outlet port 268 and pumpedthrough piping 224 to dissolved gas generators 229 and 231 where thebulk liquid is saturated with pure oxygen and dispersed into thebioreactor vessel 223 through distributor 225 from dissolved gasgenerator 229 and through distributor 228 from dissolved gas generator231. The second aeration sub system consists generally of a pump 253,two mixers applied as dissolved gas generators 238 and 241, andassociated piping. In operation bulk liquid is drawn by pump 253 fromthe bulk liquid storage tank 258 through outlet port 254 and pumpedthrough piping 246 to dissolved gas generators 238 and 241 where thebulk liquid is saturated with pure oxygen and dispersed into thebioreactor vessel 223 through distributor 242 from dissolved gasgenerator 238 and through distributor 245 from dissolved gas generator241.

[0112] The pure oxygen supply and recycling sub system supplies pureoxygen to the mixers used as dissolved gas generators 229, 231, 238, and241 for saturation of the bulk liquid as it flows through the mixers andrecycles the excess oxygen discharged from the mixers without releasingany of the oxygen to the atmosphere. The pure oxygen supply andrecycling sub system consists of a pure oxygen supply 283 with apressure regulator 282, a low-pressure storage tank 267, shutoff valves227, 232, 239, and 243 at the dissolved gas generators 229, 231, 238,and 241 respectively.

[0113] In operation, bulk liquid from the bulk liquid storage tank 258enters the dissolved gas generators 229, 231, 238, and 241 underpressure and flows through the radial grooves where the venturi drawspure oxygen from the low-pressure storage tank 267 through piping 264and saturates the bulk liquid flowing through the device with pureoxygen. Operation of the dissolved gas generators 229, 231, 238, and 241is described in detail in the discussions of FIG. 8.

[0114] The operation of the aeration system is monitor and controlled bythe controller 222. Oxygen is supplied by the gas supply and recyclingsub system as described above. The sensor 249 located in the lineupstream of pump 250 monitors the amount of dissolved oxygen in thebiomass as it flows out of the bioreactor vessel 223 and is used by thecontroller to determine the amount of dissolved oxygen remaining in thevolume of biomass in the bioreactor vessel 223. Sensors 226, 230, 240,and 244 monitor the amount of dissolved oxygen in the biomass as itflows out of each dissolved gas generator 229, 231, 238, and 241 andused by the controller 222 to determine the amount of dissolved oxygenbeing added to the biomass in the bioreactor vessel 223. By comparingthe amount of dissolved oxygen remaining in the biomass in thebioreactor vessel 223 and the amount being added by the dissolved gasgenerators 229, 231, 238, and 241 the controller can regulator the totalamount of dissolved oxygen in the biomass to within a range preset inthe controller 222 and startup or shutdown individual dissolved gasgenerators by turning the associated circulating pumps 252 or 253 on oroff and opening or closing the corresponding gas supply valves 227, 232,239, or 243. The use of dissolved oxygen for aeration alleviates theserious problem of foaming typically experienced by bubbling air throughthe systems.

[0115] The ultrafilter sub system consists generally of a pump 270 andthree ultrafilters 275, 276, and 277. In operation bulk liquid is drawnby pump 270 from the bulk liquid storage tank 258 through outlet port269 and pumped through piping 271 and through ultrafilters 275, 276, and277 and membrane interconnecting piping 278 and 272 where some of theliquid is removed by the ultrafilters and flows out of the membranesthrough piping 280. The liquid removed by the ultrafilters flows out ofthe system through piping 273. The bulk liquid from piping 280 isreturned to the bioreactor vessel 223 through inlet port 236.

[0116]FIG. 12 depicts a schematic illustration of a third embodiment ofa membrane bioreactor fluid treatment system 299 for biodegradation oforganic contaminants in wastewater in accordance with one embodiment ofthe present invention. The arrows in the piping indicate the directionof fluid flow. The membrane bioreactor fluid treatment system consistsof an equalization system 144 to merge various streams of wastewater andequalize the flowrate and contaminant level into one stream, a membranebioreactor system 300 where the biomass is concentrated andbiodegradation occurs, and a controller 222 to monitor and control theoperation. The equalization system 144 is the same equalization system144 as the one in the membrane bioreactor fluid treatment system 143illustrated in FIG. 10 and incorporated here by reference to the FIG. 10discussions.

[0117] The membrane bioreactor system 300 consists generally ofbioreactor vessel 223 in which the biodegradation occurs, an aerationsystem to supply dissolved oxygen and saturate the bulk liquid with pureoxygen to promote activity of the bacteria, a biomass separation subsystem to divide the biomass into bulk slurry and bulk liquid streams,and an ultrafilter sub system to concentrate the biomass in thebioreactor vessel 223 by removing some of the liquid and retaining allsuspended solids including bacteria. Using pure oxygen increases thesaturation concentration by approximately 4.7 times that available byusing air.

[0118] The bioreactor vessel 223, the aeration system, and the biomassseparation system are the same as those in the membrane bioreactor fluidtreatment system 219 illustrated in FIG. 11 and incorporated in thisdiscussion by reference to the FIG. 11 discussions.

[0119] The ultrafilter sub system consists generally of a pump 270 and arotating membrane ultrafilter 301. The rotating membrane ultrafilter isdiscussed below. In operation bulk liquid is drawn by pump 270 from thebulk liquid storage tank 258 through outlet port 269 and pumped throughpiping 271 and through the ultrafilter 301 where a high percentage ofthe liquid is removed by the ultrafilter and flows out of the membranesthrough piping 280. The liquid removed by the ultrafilter flows out ofthe system through piping 302. The bulk liquid from piping 280 isreturned to the bioreactor vessel 223 through inlet port 236.

[0120] FIGS. 13A-21 depict a rotating membrane ultrafilter 303 with asingle rotating membrane to illustrate the principles involved. Theshear forces created by the cross flow of a high velocity flowing fluidcan be replaced, and enhanced, by a rotating membrane in the wastewater.By rotating the membrane with a mechanical drive, differential pressureacross the membrane can be lowered, the membrane flux can be increased,and power of the pump used to cause the high velocity flow can begreatly reduced with an associated reduction in energy consumption. Theamount of liquid removed depends on the specific organic contaminants inthe wastewater; however, a much higher percentage of liquid cantypically be removed with each pass through a rotating membraneultrafilter than through a static membrane ultrafilter under the sameoperating conditions.

[0121]FIG. 13A illustrates a top view of the rotating membraneultrafilter 303 and shows where a vertical cross sectional view A-A istaken and shown in a subsequent illustration.

[0122]FIG. 13B illustrates a side elevation view of the rotatingmembrane ultrafilter 303 to identify general components. The rotatingmembrane ultrafilter 303 consists of lower housing 305, a membrane driveassembly 307, a motor 309, a wastewater inlet 306, a reject water outlet304, and a permeate outlet 308.

[0123]FIG. 14 depicts a sectional view A-A taken from FIG. 13A toillustrate internal components and fluid flow. The arrows indicate thedirection of flow. Wastewater enters the ultrafilter 303 through inlet306, flows downward around the rotating membrane 310 driven by the motor309. Liquid is removed from the stream as permeate through the membrane.The biomass is concentrated in the reject and flows out the bottom ofthe lower housing 305 through bottom outlet 304. The permeated iscollected inside the membrane 310 and flows upward through the hollowshaft of the membrane drive 307 and out through the permeate outlet 308.

[0124]FIG. 15 depicts a schematic illustration of the membrane driveassembly 307. The membrane drive assembly 307 consists of a base 316, anupper outlet 308, a shaft 314 with a membrane connection flange 320, adrive pulley 315, an upper seal 311 and bearing 312, a lower seal 319and bearing 318, and a seal 317 to seal between the membrane driveassembly 307 and the lower housing 305. The drive pulley 315 illustratedis not intended as a limitation on the type of drive mechanism used. Achain and sprocket drive or a gear drive could rotate the hollow driveshaft 314 as well.

[0125]FIG. 16 is an elevation view of the membrane 310 in the rotatingmembrane ultrafilter 303. A cross section A-A of the membrane 310 istaken and shown in the subsequent illustration.

[0126]FIG. 17 illustrates the cross section A-A of the membrane 310taken from FIG. 16. The membrane 310 consists of a porous or perforatedinner support cylinder 321, and porous membrane support 322 attached tothe inner support cylinder 321, and a thin membrane surface made bymodifying the surface of the porous membrane support 322. The innersupport cylinder may be made of perforated metal, porous sintered metal,or other material such as ceramic. The modification of the porousmembrane support 322 to make the membrane from various materials iscommercially available from a number of companies. The entire membranemay be a commercially available ceramic membrane. Rotating membraneultrafilters can be made with any number of rotating membranes. Inaddition, the rotating membrane may be used for microfilters,nanofilters, or reverse osmosis.

[0127] The surface velocity of the membrane is determined by therotating speed and the diameter of the membrane. For example, a membraneof 4.313-inch diameter rotating at 1,000 revolutions per minute wouldhave a surface velocity of approximately 18 feet per second in contactwith the wastewater. 40

[0128] FIGS. 18A-20 depict a rotating membrane ultrafilter 301 in themembrane bioreactor fluid treatment system 299 illustrated in the fluidschematic of FIG. 12. The rotating membrane ultrafilter 301 has 19membranes; however, any number of rotating membranes may be used withoutvarying from the spirit and intent of the present invention.

[0129]FIG. 18A illustrates a top view of the rotating membraneultrafilter 301 and shows where a vertical cross sectional view A-A istaken and shown in a subsequent illustration.

[0130]FIG. 18B illustrates a side elevation view of the rotatingmembrane ultrafilter 301 to identify general components. The rotatingmembrane ultrafilter 301 consists of lower housing 324, a membrane driveassembly 326, a motor 329, a wastewater inlet 325, a reject water outlet330, a permeate outlet 327, and an access panel 328 on the membranedrive assembly 326.

[0131]FIG. 19 depicts a sectional view A-A taken from FIG. 18A toillustrate internal components and fluid flow. The membranes 331 are thesame as described above. An insert 332 inside the lower housing 324forces the wastewater to flow near the rotating membranes 331 wherewater is removed and the biomass is concentrated. The arrows indicatethe direction of flow. Wastewater enters the ultrafilter 303 throughinlet 306, flows downward around the rotating membrane 310 driven by themotor 309. Liquid is removed from the stream as permeate through themembrane. The biomass is concentrated in the reject and flows out thebottom of the lower housing 305 through bottom outlet 304. The permeatedis collected inside the membrane 310 and flows upward through the hollowshaft of the membrane drive 307 and out through the permeate outlet 308.

[0132]FIG. 20 provides a view downward inside the lower housing 324 toillustrate how the rotating membranes 331 are positioned insidecylindrical passages 334 in the insert 333. Wastewater flows downwardthrough the cylindrical passages 334 adjacent to the rotating membranes331. The shearing forces caused by the rotation of the membranes 331prevent the membranes from fouling. By keeping the membranes fromfouling, a higher flux can be obtained at a lower differential pressureacross the membranes. Since wastewater velocity is not a factor a largepercentage of the inlet flow can be removed as permeate with eachpassage through the ultrafilter 301.

[0133]FIG. 21 provides an enlarged schematic illustration of themembrane drive assembly 326. The membrane drive assembly 326 consists ofa base 339, a permeate collection chamber 335, an upper outlet 327, anda hollow shaft belt drive system 337. The simple belt drive system 337illustrated is not intended as a limitation on the type of drivemechanism used. A chain and sprocket drive or a gear drive could rotatethe hollow drive shafts as well.

[0134] Biomass that cannot be consumed by bacteria, such as minerals, isperiodically purged from the system through valve 251.

What is claimed is:
 1. An apparatus for biodegradation of contaminantsin wastewater.
 2. The apparatus of claim 1 further comprising a membranebioreactor fluid treatment system.
 3. The apparatus of claim 2 furthercomprising an equalization system, a membrane bioreactor system, and acontroller.
 4. The apparatus of claim 3 in which the equalization systemcomprises a collection tank.
 5. The apparatus of claim 1 furthercomprising an aeration system.
 6. The apparatus of claim 1 furthercomprising ultrafilter subsystem.
 7. A membrane bioreactor fluidtreatment system comprising an equalization system, a membranebioreactor system, and a controller.